Enhanced Bifunctional Electrocatalysis of VN via D-Band Engineering for Rechargeable Zn-Air Batteries

The insufficient d-electron density in V metal atoms limits O₂ dissociation, constraining the kinetics and activity of the oxygen reduction reaction and the oxygen evolution reaction in VN-based catalysts. Herein, Co dopant was employed to modulate the electronic characteristics of the d-orbitals and associated free energy of VN, thereby further enhancing its catalytic activity. XPS and XANES spectra revealed that Co atoms replaced V and strongly bonded with neighboring N atoms, effectively regulating the local electronic structure. DFT analysis show that the Co doping strategy effectively regulates the adsorption/desorption equilibrium of oxygen reduction reaction intermediates through d-electron transfer to V atoms, while significantly lowering the activation energy barrier of the rate-determining step. Electrochemically, V_0.95Co_0.05N/NC/C achieved a low bifunctional index (ΔE = 0.78 V), with a half-wave potential for the ORR of 0.83 V and an OER overpotential of 380 mV at 10 mA cm^-2. In Zn-air batteries, it achieved a high specific capacity (708.98 mAh g_Zn^-1) and retained 88% initial voltage after 280 h cycling, demonstrating robust stability for practical applications. This study presents a doping strategy to modulate d-band centers in transition metal nitrides for energy conversion devices.